Gas generating agent and gas generator for automobile air bags

ABSTRACT

A gas generating agent comprising at least one compound (A) selected from the group consisting of maleic hydrazide, carbohydrazide, thiocarbohydrazide and 3-methyl-5-pyrazolone and a gas generator containing said gas generating agent. The gas generating agent may optionally comprise an oxidant and a binder.

INDUSTRIAL APPLICATION FIELD

The present invention relates to a gas generating agent and gasgenerator usable for an air bag equipped in a vehicle, such as anautomobile or aircraft, to protect human body, in which the generatedgas therefrom acts as a working gas in the air bag system.

PRIOR ART

At present, sodium azide has been mainly used in gas generatingcompositions useful for expansion of air bags. The compositions have nogreat problem regarding their combustion characteristics and have beenwidely put to practical uses. Sodium azide, however, essentially hasmany unfavorable properties. For example, having a high risk of itsexplosive decomposition and high spark sensitivity comparable to that ofblack powder, sodium azide is registered as one of B grade explosives inthe United States of America and must be handled with great care.Actually, many accidents have occurred worldwide in the process forpreparing a composition comprising sodium azide.

Additionally, the reaction of sodium azide with a heavy metal producesan salt having high impact sensitivity. Especially, the reaction withcopper produces copper azide having very high impact sensitivity. Sincecopper metal and its alloys are frequently used in materials for vehicleparts, it may possibly become social problems to scrap air bags as thenumber of vehicles to be scrapped which are equipped with air bagsincreases.

Further, sodium azide has many problems in physiological toxicity andmany cases concerning this toxicity have been reported: that is, one whohad swallowed 0.04 g of sodium azide fell down on the floor whilecomplaining of leg palsy and a violent chest pain which spread over thearms and which was similar to that of angina pectoris; and 39 years oldman who had swallowed 0.05 to 0.06 g of sodium azide suddenly faintedwith the incontinence of urine after 5 minutes and complained of nauseaand a violent headache after 10 minutes.

Furthermore, the reaction of sodium azide with an acid results in thegeneration of hydrogen azide. This has some common properties withcyanogen or hydrogen sulfide and inhibits cytochrome oxidase. Sodiumazide further causes many toxic symptoms, such as marked drop of bloodpressure, convulsions, tachycardia followed by bradycardia, andventricular fibrillation.

PROBLEMS THE INVENTION IS TO SOLVE

The invention provides a gas generating agent usable for air bags ofvehicles, which may be easily manufactured and handled because of theinclusion of no sodium azide and wherein the combustion rate may beeasily controlled and the combustion stability may be kept, and a gasgenerator containing the gas generating agent for air bags of vehicles.

MEANS FOR SOLVING THE PROBLEMS

The inventors have made great efforts to solve the abovementionedproblems and the invention has been accomplished.

The invention relates to:

(1) a gas generating agent comprising at least one compound (A) selectedfrom the group consisting of maleic hydrazide, carbohydrazide,thiocarbohydrazide and 3-methyl-5-pyrazolone;

(2) a gas generating agent comprising at least one compound (A) selectedfrom the group consisting of maleic hydrazide, carbohydrazide,thiocarbohydrazide and 3-methyl-5-pyrazolone, an oxidant and optionallya binder;

(3) the gas generating agent of (2) above, wherein said oxidant is anoxygen acid salt having a cation selected from alkali metals or alkalineearth metals and an anion which does not contain hydrogen;

(4) the gas generating agent of (3) above, wherein said oxygen acid saltis selected from the group consisting of nitrates, nitrites, chloratesand perchlorates;

(5) the gas generating agent of (1), (2), (3) or (4) above, whichcomprises 10% or more by weight of said compound (A), 90% or less byweight of said oxidant and 0 to 5% by weight of said binder;

(6) the gas generating agent of (1), (2), (3), (4) or (5) above, whereinsaid compound (A) is maleic hydrazide;

(7) the gas generating agent of (1), (2), (3), (4) or (5) above, whereinsaid compound (A) is carbohydrazide;

(8) the gas generating agent of (1), (2), (3), (4) or (5) above, whereinsaid compound (A) is thiocarbohydrazide;

(9) the gas generating agent of (1), (2), (3), (4) or (5) above, whereinsaid compound (A) is 3-methyl-5-pyrazolone;

(10) the gas generating agent of (1), (2), (3), (4) or (5) above, whichis usable for air bags of vehicles;

(11) the gas generating agent of (6) above, which is usable for air bagsof vehicles;

(12) the gas generating agent of (7) above, which is usable for air bagsof vehicles;

(13) the gas generating agent of (8) above, which is usable for air bagsof vehicles;

(14) the gas generating agent of (9) above, which is usable for air bagsof vehicles;

(15) a gas generator containing the gas generating agent of (1), (2),(3), (4) or (5) above, which is usable for air bags of vehicles;

(16) a gas generator containing the gas generating agent of (6) above,which is usable for air bags of vehicles;

(17) a gas generator containing the gas generating agent of (7) above,which is usable for air bags of vehicles;

(18) a gas generator containing the gas generating agent of (8) above,which is usable for air bags of vehicles; and

(19) a gas generator containing the gas generating agent of (9) above,which is usable for air bags of vehicles.

The gas generating agent may consist of the compound (A) or comprise thecompound (A) together with other component(s), such as an oxidant. Inthe latter, the gas generating agent preferably comprises 10% or more byweight, more preferably 15 to 90% by weight, most preferably 20 to 85%by weight, of the compound (A).

The oxidant may include various kinds of oxidants and be preferably anoxygen acid salt having a cation selected from alkali or alkaline earthmetals and an anion which does not contain hydrogen. The oxidantincludes alkali metal or alkaline earth metal salts of nitric acid, suchas lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrateand barium nitrate; alkali metal or alkaline earth metal salts ofnitrous acid, such as lithium nitrite, sodium nitrite, potassiumnitrite, magnesium nitrite and barium nitrite; alkali metal or alkalineearth metal salts of chloric acid, such as sodium chlorate, potassiumchlorate, lithium chlorate, barium chlorate, magnesium chlorate andcalcium chlorate; and alkali metal or alkaline earth metal salts ofperchloric acid, such as sodium perchlorate, potassium perchlorate,lithium perchlorate, barium perchlorate, magnesium perchlorate andcalcium perchlorate.

When the oxidant is used the gas generating agent preferably comprises90% or less by weight, more preferably 10 to 85% by weight, mostpreferably 15 to 80% by weight, of the oxidant.

A binder may be comprised in the gas generating agent and includesvarious kinds of binders, such as molybdenum disulfide. The gasgenerating agent may preferably comprise 0 to 5% by weight of thebinder. When the binder is used the gas generating agent preferablycomprises 0.1 to 5% by weight of the binder.

The gas generating agent of the invention may be obtained by mixing thecomponent(s), preferably, in the form of powder. The mixing may beperformed in the presence of water, if necessary. (When the gasgenerating agent consists of the compound (A), this compound per se isused as the gas generating agent and is preferably in powder form.) Thegas generating agent may be formed in a desired shape, for example, in agranular or pellet shape, upon use thereof. The combustion rate of thegas generating agent can be easily varied by changing a load of a pressto be applied for forming the agent and is in good consistency.

The gas generating agent of the invention is especially useful for theexpansion of an air bag equipped in a stabilizing apparatus which isinstalled in a high speed movable vehicle, such as an automobile oraircraft, and which protects a human body by expanding an air bag (gasbag) at the moment of a crash.

Upon use the gas generating agent may be packed into, for example, a gasgenerator (inflater) equipped with an ignition device. Anyconventionally known gas generator may be used. For example,conventional gas generators made of iron, aluminium, copper, variousalloys or plastics and in cylindrical, hemispherical or spherical shapemay be used. Further, the gas generator provided with holes in asuitable diameter or baffles may be used to control the direction andvelocity of the generated gas flowing therefrom.

The gas generating agent packed into the gas generator may be ignited bymeans of a conventional way, for example, an electric current applied ormechanical impact. The gas generating agent is burnt by ignition and thegas then generated is fed into an air bag to expand the bag.

The compound (A) contained in the gas generating agent of the inventionis very excellent in combustion properties demanded for an air bag: thatis, the combustion rate of the gas generating agent varies linearly withthe bulk density thereof and therefore easily controlled; the gasgenerating agent is stable in the combustion rate and excellent inprolonged stability with time; and further the volume of the gasgenerated per unit weight of the gas generating agent is far larger incomparison with that of the gas from sodium azide.

Additionally, handling of the compound (A) is very easy. In sodiumazide, complete prevention of its moisture absorption is inevitable dueto its hygroscopicity and toxicity of hydrogen azide generated fromsodium azide. On the contrary, the gas generating agent of the inventionbased on the compound (A) has very low hygroscopicity and there islittle necessity of preventing moisture absorption.

Furthermore, the compound (A) is very safe in comparison with sodiumazide regarding toxicity: LD₅₀ of maleic hydrazide (CAS No. 123-33-1) inoral administration to rat being 3800 mg/kg, LD₅₀ of carbohydrazide (CASNo. 497-18-7) in intravenous injection to mouse being 120 mg/kg but LD₅₀of sodium azide (CAS No. 26628-22-8) in oral administration to mousebeing 27 mg/kg; further LDL0 of 3-methyl-5-pyrazolone (CAS No. 108-26-9)in rat being 600 mg/kg but LDL0 of sodium azide (CAS No. 26628-22-8) inoral administration to mouse being 42 mg/kg. The compound (A) is farexcellent in safety.

The compound (A) or a mixture thereof with other component(s) may bepressed to obtain aggregated pellets having enough strength as the gasgenerating agent for an air bag even in the absence of binder. A smallportion of the binder, however, may be added to the gas generatingagent. When a potassium salt is present in the gas generating agent theparticularly preferred binder is molybdenum disulfide.

As shown in Examples, the combustion rate of the gas generating agentmay be easily varied by changing a load of a press to be applied for theforming thereof and is in good consistency. Additionally, the gasgenerating agent of the invention is excellent in prolonged heatstability with time and has good reliability. Thus, the gas generatingagent of the invention well satisfies the characteristics required whenused in an inflater.

EXAMPLE

Hereinafter, the present invention will be illustratively explained withExamples.

Examples 1A to 6A

In the proportions shown in Table 1A, maleic hydrazide (MH) and anoxidant in powder form were homogeneously mixed by using a V-shapedmixer. The mixture was transferred into a mortar of 10 mm or 6 mm indiameter and pressed at a load of 600 kg/cm² or 300 kg/cm² to formpellets. The weight per pellet thus obtained is shown in Table 1A.

                                      TABLE 1A                                    __________________________________________________________________________         MH           Oxidant Diameter                                                                           Load Weight per                                Examples                                                                           (% by Weight)                                                                         Oxidant                                                                            (% by Weight)                                                                         (mm) (kg/cm.sup.2)                                                                      Pellet(g)                                 __________________________________________________________________________    1A   25.5    KClO.sub.3                                                                         74.5    10   600  1.00                                      2A   25.5    KClO.sub.3                                                                         74.5    10   600  0.50                                      3A   25.5    KClO.sub.3                                                                         74.5    6    300  0.25                                      4A   25.5    KClO.sub.3                                                                         74.5    6    600  0.25                                      5A   28.8    KClO.sub.4                                                                         71.2    6    600  0.25                                      6A   28.8    KClO.sub.4                                                                         71.2    6    600  0.15                                      __________________________________________________________________________

8.0 g or 7.5 g of the pellets thus obtained was packed into a bomb of 1Land ignited with a squib which comprised 3 mg of a fuse head consistingof diazodinitrophenol (DDNP) and 0.6 g of an igniter consisting ofboron/potassium nitrate mixture (25/75). The relationship betweenincreases in the pressure of the bomb and elapsed times was plotted anda time during which the pressure of the bomb was increasing wasdesignated as a combustion time. Using the pellets obtained by the samemanner as described above, experiments described above were repeatedfurther three times and the combustion times obtained in each experimentare shown in Table 2A. As shown in Table 2A, the combustion times werewell constant.

                  TABLE 2A                                                        ______________________________________                                        Weight of        Combustion Time (ms)                                         Examples                                                                              Pellets Used(g)                                                                            1st    2nd    3rd  4th                                   ______________________________________                                        1A      8.0          89     88     91   92                                    2A      7.5          55     56     57   56                                    3A      7.5          37     36     35   36                                    4A      7.5          49     48     49   47                                    5A      7.5          44     43     44   42                                    6A      7.5          29     29     28   30                                    ______________________________________                                    

The number of moles of the gas generated by combustion of each gasgenerating agent in each Example was measured. Each gas generating agentof Example 1A, of Examples 2A to 4A or of Examples 5A and 6A generated0.128 mol, 0.120 mol or 0.135 mol of the gas, respectively.

Example 7A

7.5 g of the pellets in Example 6A was burnt in the same manner asdescribed in Example 1A after being kept at 120° C. for 240 hours tomeasure the quality thereof after storage at a high temperatureenvironment. The obtained combustion times were 29, 28, 29 and 30 ms andwere in good consistency as those of Example 6A.

Examples 1B to 6B

In the proportions shown in Table 1B, carbohydrazide (CH) and an oxidantin powder form were homogeneously mixed by using a V-shaped mixer. Themixture was transferred into a mortar of 10 mm or 6 mm in diameter andpressed at a load of 600 kg/cm² or 300 kg/cm² to form pellets. Theweight per pellet thus obtained is shown in Table 1B.

                                      TABLE 1B                                    __________________________________________________________________________         CH           Oxidant Diameter                                                                           Load Weight per                                Examples                                                                           (% by Weight)                                                                         Oxidant                                                                            (% by Weight)                                                                         (mm) (kg/cm.sup.2)                                                                      Pellet (g)                                __________________________________________________________________________    1B   30.6    KClO.sub.3                                                                         69.4    10   600  1.00                                      2B   30.6    KClO.sub.3                                                                         69.4    10   600  0.50                                      3B   30.6    KClO.sub.3                                                                         69.4    6    300  0.25                                      4B   30.6    KClO.sub.3                                                                         69.4    6    600  0.25                                      5B   34.2    KClO.sub.4                                                                         65.8    6    600  0.25                                      6B   34.2    KClO.sub.4                                                                         65.8    6    600  0.15                                      __________________________________________________________________________

8.0 g or 7.5 g of the pellets thus obtained was packed into a bomb of 1Land ignited with a squib which comprised 3 mg of a fuse head consistingof diazodinitrophenol (DDNP) and 0.6 g of an igniter consisting ofboron/potassium nitrate mixture (25/75). The relationship betweenincreases in the pressure of the bomb and elapsed times was plotted anda time during which the pressure of the bomb was increasing wasdesignated as a combustion time. Using the pellets obtained by the samemanner as described above, experiments described above were repeatedfurther three times and the combustion times obtained in each experimentare shown in Table 2B. As shown in Table 2B, the combustion times werewell constant.

                  TABLE 2B                                                        ______________________________________                                        Weight of        Combustion Time (ms)                                         Examples                                                                              Pellets Used(g)                                                                            1st    2nd    3rd  4th                                   ______________________________________                                        1B      8.0          141    140    143  142                                   2B      7.5          105    106    107  106                                   3B      7.5           67     66     65   66                                   4B      7.5           89     88     89   87                                   5B      7.5          116    119    117  117                                   6B      7.5           81     80     79   81                                   ______________________________________                                    

The number of moles of the gas generated by combustion of each gasgenerating agent in each Example was measured. Each gas generating agentof Example 1B, of Examples 2B to 4B and of Examples 5B and 6B generated0.163 mol, 0.153 mol and 0.171 mol of the gas, respectively.

Example 7B

7.5 g of the pellets in Example 6B was burnt in the same manner asdescribed in Example 1B after being kept at 120° C. for 240 hours tomeasure the quality thereof after storage at a high temperatureenvironment. The combustion times thus measured were 78, 82, 81 and 80ms and were in good consistency as those of Example 6B.

Examples 1C to 6C

In the proportions shown in Table 1C, thiocarbohydrazide (TCH) and anoxidant in powder form were homogeneously mixed by using a V-shapedmixer. The mixture was transferred into a mortar of 10 mm or 6 mm indiameter and pressed at a load of 600 kg/cm² or 300 kg/cm² to formpellets. The weight per pellet thus obtained is shown in Table 1C.

                                      TABLE 1C                                    __________________________________________________________________________         TCH          Oxidant Diameter                                                                           Load Weight per                                Examples                                                                           (% by Weight)                                                                         Oxidant                                                                            (% by Weight)                                                                         (mm) (kg/cm.sup.2)                                                                      Pellet(g)                                 __________________________________________________________________________    1C   27.0    KClO.sub.3                                                                         73.0    10   600  1.00                                      2C   27.0    KClO.sub.3                                                                         73.0    10   600  0.50                                      3C   27.0    KClO.sub.3                                                                         73.0    6    300  0.25                                      4C   27.0    KClO.sub.3                                                                         73.0    6    600  0.25                                      5C   30.4    KClO.sub.4                                                                         69.6    6    600  0.25                                      6C   30.4    KClO.sub.4                                                                         69.6    6    600  0.15                                      __________________________________________________________________________

8.0 g or 7.5 g of the obtained pellets was packed into a bomb of 1L andignited with a squib which comprised 3 mg of a fuse head consisting ofdiazodinitrophenol (DDNP) and 0.6 g of an igniter consisting ofboron/potassium nitrate mixture (25/75). The relationship betweenincreases in the pressures of the bomb and elapsed times was plotted anda time during which the pressure of the bomb was increasing wasdesignated as a combustion time. Using the pellets obtained by the samemanner as described above, experiments described above were repeatedfurther three times and the combustion times obtained in each experimentare shown in Table 2C. As shown in Table 2C, the combustion times werewell constant.

                  TABLE 2C                                                        ______________________________________                                        Weight of        Combustion Time (ms)                                         Examples                                                                              Pellets Used(g)                                                                            1st    2nd    3rd  4th                                   ______________________________________                                        1C      8.0          139    138    141  142                                   2C      7.5          65     66     67   66                                    3C      7.5          47     46     45   46                                    4C      7.5          69     68     69   67                                    5C      7.5          126    129    127  127                                   6C      7.5          91     90     89   91                                    ______________________________________                                    

The number of moles of the gas generated in combustion of each gasgenerating agent in each Example was measured. Each gas generating agentof Example 1C, of Examples 2C to 4C and of Examples 5C and 6C generated0.143 tool, 0.134 mol and 0.151 mol of the gas, respectively.

Example 7C

7.5 g of the pellets in Example 6C was burnt in the same manner asdescribed in Example 1C after being kept at 120° C. for 240 hours tomeasure the quality thereof after storage at a high temperatureenvironment. The combustion times thus measured were 88, 92, 91 and 90ms and were in good consistency as those of Example 6C.

Examples 1D to 6D

In the proportions shown in Table 1D, 3-methyl-5-pyrazolone (MP) and anoxidant in powder form were homogeneously mixed by using a V-shapedmixer. The mixture was transferred into a mortar of 10 mm or 6 mm indiameter and pressed at a load of 600 kg/cm² or 300 kg/cm² to formpellets. The weight per pellet thus obtained is shown in Table 1D.

                                      TABLE 1D                                    __________________________________________________________________________         MP           Oxidant Diameter                                                                           Load Weight per                                Examples                                                                           (% by Weight)                                                                         Oxidant                                                                            (% by Weight)                                                                         (mm) (kg/cm.sup.2)                                                                      Pellet(g)                                 __________________________________________________________________________    1D   19.3    KClO.sub.3                                                                         80.7    10   600  1.00                                      2D   19.3    KClO.sub.3                                                                         80.7    10   600  0.50                                      3D   19.3    KClO.sub.3                                                                         80.7    6    300  0.25                                      4D   19.3    KClO.sub.3                                                                         80.7    6    600  0.25                                      5D   22.0    KClO.sub.4                                                                         78.0    6    600  0.25                                      6D   22.0    KClO.sub.4                                                                         78.0    6    600  0.15                                      __________________________________________________________________________

8.0 or 7.5 g of the pellets thus obtained was packed into a bomb of 1Land ignited with a squib which comprised 3 mg of a fuse head consistingof diazodinitrophenol (DDNP) and 0.6 g of an igniter consisting ofboron/potassium nitrate mixture (25/75). The relationship betweenincreases in the pressure of the bomb and elapsed times was plotted anda time during which the pressure of the bomb was increasing wasdesignated as a combustion time. Using the pellets obtained by the samemanner as described above, experiments described above were repeatedfurther three times and the combustion times obtained in each experimentare shown in Table 2D. As shown in Table 2D, the combustion times werewell constant.

                  TABLE 2D                                                        ______________________________________                                        Weight of        Combustion Time (ms)                                         Examples                                                                              Pellets Used(g)                                                                            1st    2nd    3rd  4th                                   ______________________________________                                        1D      8.0          85     85     87   86                                    2D      7.5          50     51     52   51                                    3D      7.5          41     42     40   42                                    4D      7.5          46     46     45   44                                    5D      7.5          37     36     38   37                                    6D      7.5          31     32     31   30                                    ______________________________________                                    

The number of moles of the gas generated by combustion of each gasgenerating agent of each Example was measured. Each gas generating agentof Example 1D, of Examples 2D to 4D and of examples 5D and 6D generated0.126 mol, 0.119 mol and 0.135 mol of the gas, respectively.

Example 7D

7.5 g of the pellets in Example 6D was burnt in the same manner asdescribed in Example 1D after being kept at 120° C. for 240 hours tomeasure the quality thereof after storage at a high temperatureenvironment. The combustion time thus measured were 31, 32, 30 and 30 msand were in good consistency as those of Example 6D.

Example 1E

Each of the pellets obtained in Examples 1A to 6A, 1B to 6B, 1C to 6Cand 1D to 6D was examined by a combustion test wherein a knowncylindrical gas generator provided with an ignition device for air bagsof vehicles was packed with each of the pellets. In all instances, thecombustion rate thereof and the volume of the generated gas therefromsuitable for air bags of vehicles were obtained.

EFFECT OF THE INVENTION

As containing the compound (A) easy to be handled and having very lowtoxicity instead of sodium azide which is dangerous in its handling andphysiologically harmful, the gas generating agent of the invention hasgood combustion stability required in an inflater.

What is claimed is:
 1. A gas generating agent for air bags of vehicles,comprising at least one compound (A) selected from the group consistingof maleic hydrazide, carbohydrazide, and 3-methyl-5-pyrazolone, anoxidant comprising a chlorate or perchlorate having a cation selectedfrom the group consisting of alkali metals and alkaline earth metals,and. optionally a binder.
 2. The gas generating agent of claim 1, whichcomprises 10% or more by weight of said compound (A), 90% or less byweight of said oxidant and 0 to 5% by weight of said binder.
 3. The gasgenerating agent of claim 1 or 2, wherein said compound (A) is maleichydrazide.
 4. The gas generating agent of claim 1 or 2, wherein saidcompound (A) is carbohydrazide.
 5. The gas generating agent of claim 1or 2, wherein said compound (A) is 3-methyl-5-pyrazolone.
 6. A vehicleair bag gas generator comprising a gas generating agent comprising atleast one compound (A) selected from the group consisting of maleichydrazide, carbohydrazide and 3-methyl-5-pyrazolone, an oxidantcomprising a chlorate or perchlorate having a cation selected from thegroup consisting of alkali metals and alkaline earth metals, andoptionally a binder; and means for igniting said gas generating agent.7. The vehicle air bag gas generator of claim 6, which comprises 10% ormore by weight of said compound (A) , 90% or less by weight of saidoxidant and 0 to 5% by weight of said binder.
 8. The vehicle air bag gasgenerator of claim 6 or 7, wherein said compound (A) is maleichydrazide.
 9. The vehicle air bag gas generator of claim 6 or 7, whereinsaid compound (A) is carbohydrazide.
 10. The vehicle air bag gasgenerator of claim 6 or 7, wherein said compound (A) is3-methyl-5-pyrazolone.